It's cold outside, but not early enough or long enough to kill off all invasive species

The unusually cold temperatures haven't lasted long enough to kill off all invasive species, according to a report from the U.S. Forest Service and the Minnesota Department of Agriculture, Lacee Shepard reports for the Capital News Service, based at Michigan State University. (Flickr photo: Emerald ash borer)

The report found that when temperatures hit -10 F., some invasive species, such as the emerald ash borer, which feeds on ash and kills the tree, could freeze to death, Shepard writes. But like many insects, the borer adjusts to the weather, and adjusts to survive. Thus, though this winter has been cold, it turned extremely cold too late to eliminate the species.

“Insects go through a physiologically intense process of acclimatization in the fall and there’s actually changes in their bodies. It’s the equivalent of having antifreeze," Deborah McCullough, a professor of entomology and forestry at Michigan State, told Shepard. "If the insects don’t create this antifreeze their cells will freeze and burst, killing them. If we had this Arctic vortex the first or second week of November, it might have been really different. But there have been all these weeks of cooler and cooler temperatures for the ash borer larvae, under the bark, to have acclimatized. Because it’s the middle of winter they are as acclimatized as they could possible be. Some of them are still going to survive it.”

Still, McCullough said she hopes "the cold will kill off other harmful species like mimosa webworm, an insect that webs leaves together and feeds on them," Shepard writes. "While the harm they cause is less severe than what emerald ash borer or the (hemlock woolly adelgid) cause, it is still damaging and unsightly." The hemlock woolly adelgid preys on hemlock by injecting toxic saliva while feeding, eventually killing the tree. The species appeared to vanish in 2006, but made a comeback in 2013. (Read more)